1. Field of the Invention
The present invention relates to apparatus for stopping the motor of a motor drive mechanism in a camera.
2. Description of the Prior Art
The motor drive mechanism in a camera is provided to drive a motor for winding up the film. The motor is started by means of a film winding start signal, and stopped by means of a film winding end signal. Usually, the film winding start signal is formed by a signal indicating that a shutter operation has come to end and the film winding end signal is formed by a signal indicating that the winding of one frame length of film has been completed.
The above-mentioned type of motor drive mechanism involves an important problem. In the motor drive mechanism, the motor continues to rotates unless the signal indicating completion of film winding is generated properly. Therefore, if a malfunction occurs such that the film is wound beyond the last frame of the useful length of the film, or if the film is jammed during winding, the motor would be overloaded. In this case, the motor produces an excessively large force which may break the perforations of the film.
To solve the problem it has already been proposed to detect an overcurrent condition in the motor and stop the motor by means of the detection signal. However, there are various types of films in the market and generally different levels of film feeding torque are applied to different types of films. Since the above known solution uses, as the reference current value, a certain predetermined value common to all of different films to stop the motor, it is very difficult to properly stop the motor before the film perforation is broken for all types of films.
As another solution to the above problem, it has been also proposed to preset a desired number of film frames at a counter and mechanically stop the motor when the number of pictures taken by the camera reaches the preset number. According to the second solution, it is possible to stop the motor without fail after a certain number of picture have been taken. However, this solution imposes upon users of the camera the requirement of presetting for each roll of film the number prior to beginning photography. In addition, even employing this solution there still remains unsolved the problem that the motor may be overloaded in the event of film jamming.